Yasuhisa Senda

The conformational study of chitin and chitosan oligomers in solution

The inter-residual dihedral angles phi and phip of chitin and chitosan oligomers were determined from experimental 3J(C-H) constants and ROESY cross peaks.

cis-1-Amino-1,2,3,4-tetrahydro-2-naphthalenol: resolution and application to the catalytic enantioselective reduction of ketones

Abstract cis -1-amino-1,2,3,4-tetrahydro-2-naphthalenol was synthesized and resolved via its diastereomeric salts. Asymmetric reduction of prochiral ketones was examined using this amino alcohol at various temperatures.

Controlling factors determining the regiochemistry of intramolecularalkoxymercuration

The intramolecular alkoxymercuration of n(E)-5-arylpent-4-en-1-ols indicated that the nregioselectivity is closely related to the Hammett constants of the npara-substituents on the benzene ring. Large solvent effects on nthe regioselectivity were also observed. These results were compared nwith those of the methoxymercuration of β-methylstyrene analogues. nThe regioselectivity is discussed in terms of steric effects as well as nthe electronic effects which are suggested by the MO calculation for the nmercurinium ion intermediates.

A probe of Cieplak's proposal: effect of 2-axial substitution on reactivity in the LiAlH4 reduction of cyclohexanones

The relative reactivities of cyclohexanones in which the 2-axial position is substituted by methyl or methoxy group in LiAlH4 reduction strongly support the Cieplak model which focuses on the importance of stabilisation of the transition state by antiperiplanar allylic bonds.

Regio- and stereoselectivity in the solvomercuriation and intramolecular alkoxymercuriation of cyclic unsaturated alcohols

The regio- and stereoselectivity in the solvomercuriation and intramolecular alkoxymercuriation of several cyclic olefinic alcohols were examined. The regioselectivity is controlled mainly by electronic factors, while the stereoselectivity is controlled by steric factors as well as electronic ones. The optimised structure of the mercurinium ion intermediate suggests that the attractive interaction between the hydroxy group in the molecule and the mercurinium ion moiety affects the selectivity.

The role of the nitrogen atom in the hydrogenation of piperidinones and methylenepiperidines

Dimethylpiperidinones and dimethylmethylenepiperidines have been hydrogenated over several Group 8, 9 and 10 transition metal catalysts and the stereochemistry of the products compared with those of the carbocyclic analogues. The results obtained suggest that intramolecular interactions between the nitrogen lone pair and the unsaturated bond play a major role in determining the stereochemistry of hydrogenation.